The goal is to clarify the influence of function on the growth and ultimate morphology of the head. The proposed studies focus on the muscles of mastication using the miniature pig as a model for human jaw function. Major areas of interest for the next project period will be the cranial sutures, the primary loci of skull deformation during function, and the architecture of newly formed periosteal bone, an important determinant of cranial strain. The addition of vital staining and immunocytochemical techniques provide a new emphasis on growth events at the cellular level and their correlation with function. Specific Aim 1 continues the investigation of dynamic stress transmission. In vivo strain gage recordings will be used to investigate bite force and facial bending. Pressure transducers and vital labeling will be used to test the hypothesis that higher pressures lead to surface resorption. Specific Aim 2 will measure the mechanical properties of the periosteum. Tensile testing will be used to look for regional and directional differences in stiffness that could influence loading, and hence growth. Specific Aim 3 will explore the relationships among sutural strain, morphology, growth and fusion. Sutures of differing morphology will be compared using in vivo recording and vital labeling. Morphological complexity is expected to be associated with compressive strain and low growth rates. The naturally fusing interparietal suture will serve to evaluate the effect of fusion on surrounding bones. Specific Aim 4 will investigate the biomechanical consequences and cellular basis for bone microstructure in the zygomatic arch. Periosteal cell kinetics and matrix organization will be examined to understand regional differences in bone deposition patterns. The general principles of how periostea and sutures respond to loads by differential growth are applicable to human function at all levels. Because work on pigs has enabled the Principal Investigator to interpret bony structure biomechanically, she is now ready to extend this work to humans. Specific Aim 5 will quantify the architecture of the human zygomatic arch and condyle. Collectively, these findings pertain to clinical problems related to abnormal biomechanics, such as facial deformities , consequences of myopathies, trauma repair, and predicting the results of orthognathic surgery.